It is in many circumstances encountered in a wide variety of activities difficult to align two connecting parts of a connector assembly for proper connection. A particular example of such circumstances is the attachment to undersea anchors of tubular or otherwise hollow members suspended from the surface, particularly if the water depth is large. This type of problem is frequently encountered in the exploitation of undersea gas and oil reserves, particularly in the guidance and connection of compliant vertical marine structures, e.g. single anchor leg moorings, articulated columns, tension leg platform moorings, to a seabed foundation.
Offshore oil and gas fields have been developed in water depths to 200 meters, which is generally considered to be the working limit for divers in flexible suits and who are therefore subjected to ambient pressure of about 21 atmospheres. Well drilling has progressed to water depths up to 1500 meters, and remotely-controlled vehicles (RCV's) with television cameras and manipulators have been developed for performing work required below 200 meters depth. RCV's may also replace divers for many tasks in shallower water.
Structures for the support of wellheads, separation, gas flaring, and tanker loading equipment have been designed, and in the cases of gas flaring and tanker loading installed, which have a compliant or articulating connection to a seabed foundation and depend on buoyancy to maintain the structure in a close to vertical, stable configuration. These structures are generally more feasible for installation in deeper water than fixed structures which do not have buoyancy, and which depend on their own stiffness and strength to support equipment.
For some compliant structures, the seabed foundation is installed prior to structure arrival on site. The foundation may be of a gravity type, i.e. dependent on selfweight to maintain position, or piled, either by driving or drilling. Means are usually provided on the foundation to allow the structure to connect to it.
The structure is generally hollow and sufficiently long to extend from the seabed to the surface. When the structure arrives on site, it will usually have a universal joint (e.g. a Hooke's joint or a bonded rubber flexjoint) and connector attached at the lower end, and may be floating in a horizontal position on the surface. Buoyancy adjustment along the structure length will allow it to swing from the horizontal to vertical position so that the universal joint and connector are some tens of feet above the seabed.
Once in the vertical position, floating or virtually suspended over the foundation, wind and current forces must be counteracted to prevent drifting. Surface vessels with lines attached to the structure can maintain it within a radius of tens of feet around the correct position directly over the foundation connection point by using sonar transponders.
To make a successful connection between the lower part of the universal joint and the foundation, the former must be brought to a position directly above the connection means mounted on the latter. It is also preferable for the connector of the lower part of the universal joint, and the connection means on the foundation, to be correctly aligned both laterally and angularly, before mating. These operations should not involve the use of divers, and should be practically independent of water depth.